A team from the Vision Institute (L’Institut de la Vision) demonstrated that an artificial retina, an implant placed at the level of the retina that receives an image directly from the photosensitive cells, would induce high-resolution visual perception. Their results have paved the way for clinical trials for the treatment of age-related macular degeneration and possibly retinitis pigmentosa.
For several years, the prospect of restoring vision in patients with age-related macular degeneration (AMD) or retinitis pigmentosa has become increasingly tangible. AMD is a particularly debilitating disease, characterized by degradation of the retina that can lead to loss of central vision. According to Inserm (Institut national de la santé et de la recherche médicale), it is the leading cause of visual impairment among people over the age of 50. “All forms combined, this disease affects approximately 8% of the population, but its frequency increases with age. It affects 1% of people aged 50 to 55, 10% of those aged 65 to 75, and 25% to 30% of those over 75,” says the Institute.
For years, researchers have been working to develop an artificial retina that could restore sight to these patients, as well as to patients with retinitis pigmentosa. This genetic disease, which affects one in 4,000 people, is characterized by progressive degeneration of photoreceptors in the retina that convert light signals into electrical signals to the brain. The retina is composed of photosensitive cells and photoreceptors, whose purpose is to transform light signals received by the eye into electrical signals which are then sent to the brain. These cells are destroyed during these pathologies, which can cause blindness.
Obtaining an increasingly accurate image
The principle of an artificial retina is to replace these photoreceptors. The device consists of implants fixed under the retina and electrode compounds that stimulate retinal neurons to carry messages to the brain. Two of these devices, Argus II and Retinal Implant, have already been widely implanted. “However, these two companies are gradually withdrawing from the market. Patients could see luminous signs, but those who could distinguish the letters were a very small minority,” says Serge Picaud, a researcher at Inserm.
His team wanted to reinvent the system to make it more effective. Developed in collaboration with the company Pixium Vision, its artificial retina is a wireless device that is less complex, unlike the previous devices. It has the advantage of introducing feedback from the local current, thus inducing a better resolution of the images perceived by the eye. Finally, the image is projected onto the implant by means of infrared stimulation that activates photodiodes connected to the electrodes, for more direct stimulation of the neurons of the retina. In a study published in Nature Biomedical Engineering, researchers tested this device in primates, demonstrating that it restored visual acuity.
Towards implantation in patients
In vitro tests showed that each pixel activates different cells in the retina. “This selectivity results in a very high resolution, so that implanted animals can perceive the activation of a single implant pixel in a behavioral test,” the researchers say. These good results paved the way for the implantation of devices in five French patients with AMD. Initial results indicate that they are gradually regaining central vision: they are able to perceive luminous signals, and some can even identify letter sequences, faster and faster over time.
“The goal now is to conduct a phase 3 study in a larger group of patients with age-related macular degeneration. If the artificial retina works in them, we believe there is no reason why it shouldn’t work in patients suffering from retinitis pigmentosa, a disease also related to photoreceptor degeneration,” concludes Serge Picaud. Currently, only the wet form of AMD (the other form being dry or atrophic) is treated with antiangiogenic drugs, whose function is to interrupt the progression of the disease. Several injections are needed at a pace defined by the ophthalmologist.